Task priority change info missing in Firehose Webhook?

I configured a Firehose webhook in Herald, and I’m able to receive the events when I modify the owner or status of my tasks.
Nonetheless, changing the priority of a task is generating an event from which I can’t tell it’s the priority what changed.

This is the incoming message:

    "object": {
        "type": "TASK",
        "phid": "PHID-TASK-ohdiwmnsg6yafpobnqdq"
    "triggers": [
            "phid": "PHID-HWBH-c5z5bjus623e7nsjgndf"
    "action": {
        "test": false,
        "silent": false,
        "secure": false,
        "epoch": 1535085157
    "transactions": [
            "phid": "PHID-XACT-TASK-zg53pgpct77m5fx"

when I query that transaction with transaction.search I get this:

    "id": 68,
    "phid": "PHID-XACT-TASK-zg53pgpct77m5fx",
    "type": null,
    "authorPHID": "PHID-USER-r3axkdu63rznqohq3r4b",
    "objectPHID": "PHID-TASK-ohdiwmnsg6yafpobnqdq",
    "dateCreated": 1535085156,
    "dateModified": 1535085156,
    "comments": [],
    "fields": {}

Notice the type is null, while in other transaction types it has the name of the field that changed.

Is this a missing feature?

I enriched this result in https://secure.phabricator.com/D19599.

This change is available in master and should promote to stable in 2018 Week 34 later today.

I just tested it and it works fine.